The present invention relates to aircraft electric power distribution systems (EPDS) and methods for improving lightning strike immunity thereof and, more specifically, to apparatus and methods for preventing undesirable trips of a solid state power controller (SSPC).
Solid state power controllers (SSPC) are widely used in secondary electrical power distribution systems (SEPDS) in modern aircrafts due to their high reliability, “soft” switching characteristics, fast response time, and ability to facilitate advanced load management and other aircraft functions. Typically an SSPC is provided with over-current fault and arc fault detection and protection mechanisms to ensure the safety of the aircraft EPDS. One of the main challenges in designing the SSPC, which is mainly electronics circuitry based, is to ensure that its intended functions will not be upset by transients induced during lightning strikes. These lightning induced transients in load currents sometimes bear similar patterns to those resulting from arcs or over current faults.
A typical aircraft may be equipped with electrical distribution systems that are robust enough and suitably protected to tolerate lightning induced transients. Nevertheless, a lightning induced transient may cause tripping of an SSPC. In other words, the SSPC may experience a lightning-induced nuisance trip.
Nuisance trips of an SSPC are problematic because safety standards for aircraft operation require that an SSPC that is tripped during flight may be reset only after the aircraft is no longer in flight. Thus, even though an aircraft may endure in-flight lightning strikes without harm, there is the possibility that one or more of its electrical distribution circuits may become inoperative as a result of nuisance trips of one or more of its SSPCs.
As can be seen, there is a need for a system in which lightning-induced current surges may be differentiated from arcing and short circuit faults in an EPDS. More particularly, there is a need for a system in which tripping of an SSPC may be avoided if an overcurrent condition arises because of a lightning strike.